The present invention idea relates to amine-based hydrophobically modified alkylene oxide urethane polymers as rheology modifiers, which are especially useful in architectural coatings.
Rheology modifiers are typically designed to impart desirable rheological properties to coating formulations over a wide shear rate range. U.S. Pat. No. 7,741,402 discloses ethylene oxide urethane polymers modified with hydrophobes that contain organic bases such as secondary or tertiary amines (amine-modified HEURs), the presence of which provides for viscosity control through a pH trigger. When the pH of the HEUR composition is sufficiently low with respect to the pKa of the incorporated base, the basic groups are protonated and the viscosity is relatively low; when the pH is sufficiently high, associative thickening occurs. Thus, incorporation of basic hydrophobes into the HEUR polymer allows relatively high concentration of polymer to be dissolved in water at low pH; once the solution is added to the high pH environment of paint coatings, the base is deprotonated and the associative thickening mechanism activated.
Amine-modified HEURs can be sensitive to the pH of the paint formulation to which it is added. For example, the pH of the formulation, through time and heat aging, may decrease to a level below a critical pH conducive to associative thickening, thereby resulting in a poorer formulation; consequently, it would be desirable to discover a hydrophobe, more particularly an amine-based hydrophobe, that preserves the desired viscosity of the formulation in face of pH-lowering mechanisms.